Level Of Rennet Research Articles

Structural dependence of concentrated skim milk curd on micellar restructuring

This study was conducted to establish an understanding of how milk concentration modulates the rennet curd structure. Rennet-induced gelation and renneting under slow acidification achieved using glucono-δ-lactone (GDL) and structural properties of reconstituted skim milk gels at two concentration levels (9 and 25 % total solids) were studied by measuring variations in (a) viscoelastic behaviour, (b) micellar size, charge density, diffusivity, and (c) hydrophobicity using dynamic rheometry, dynamic light scattering and fluorimetry, respectively. Concentrated milk showed a greater estimated hydrodynamic radius of casein micelles, lower zeta (ζ)-potential, ratio of serum to total Calcium (Ca) and charge density and increased surface hydrophobicity, all supporting the view that micellar restructuring particularly sub-particle transfer takes place and contributes to rapid gelation. Moreover, hydrophobic interactions occurred very quickly (within 5 min in combined gels, 10 min for renneting only), demonstrating their pivotal role during the flocculation stage. All gels exhibited a solid viscoelastic character as the elastic modulus (G′) was greater than loss modulus (G″) while both G′ and tan δ (G''/G′) were frequency-dependent. Frequency sweeps classified the concentrated gels into three stiffness categories caused by the level of rennet or GDL as rigid, hard and soft, whereas an increased flow-like behaviour (high tan δ), restricted diffusion and excessive water retention revealed limited structural rearrangements (contraction & macrosyneresis) during curd ageing. Acidification increased the diffusion rate in control curd, thus, enhanced contractive rearrangements, macrosyneresis and curd strength. Findings suggest that micellar restructuring induced by milk concentration is the principal modulator of the curd structure.

Rennet coagulation properties of milk in the presence of oil droplets stabilised by a combination of sodium caseinate and whey protein isolate

This manuscript describes the in situ investigation of the rennet-induced aggregation of skim milk recombined with emulsion droplets stabilised with whey protein isolate (WPI) and sodium caseinate (NaCas) in isolation or in combination. The experiments were conducted with two levels of rennet as well as with and without added CaCl2. Diffusing wave spectroscopy and small deformation rheology were used to follow the gelation behaviour. In addition, scanning electron microscopy was employed to observe changes in the aggregation state of the oil droplets. We report that the presence of WPI-stabilised droplets did not alter the gelation behaviour of the casein micelles in recombined milks, even in the presence of added CaCl2. In contrast, NaCas-stabilised droplets in solution impaired the rennetability of the recombined milk, even after the addition of CaCl2. The mixture of both proteins at the interface was also investigated. When the WPI covering the fat droplets was gradually and systematically substituted by NaCas, any amount over 30% also impaired the rennetability of the milks. It was speculated that the increased steric repulsion of the oil droplets in conjunction with an increase in NaCas present in the serum phase in the recombined milks were the most likely contributors to the impaired rennetability of the casein micelles.

Characterization of rennet coagulation of milk concentrated by vacuum condensing and ultrafiltration

A comparison of rennet coagulation of milk supplemented with vacuum-condensed or ultrafiltered milk was undertaken. Five treatments with two levels of protein (45 and 60 g·kg−1) from vacuum-condensed (CM1 and CM2) and ultrafiltered milk (UF1 and UF2) along with a 32 g·kg−1 protein control were compared. A Formagraph was used to characterize rennet clotting time (RCT), amplitude at 40 min (a40), and time to achieve amplitude of 20 mm (k20). Rennet was added at 192 μL·kg−1 milk, without prior addition of starter. RCT was lower for CM than for UF, and lower for higher protein milks. The k20 values were lower for higher protein samples, indicating a higher rate of curd firming; and were not affected by the method of concentration. The a40 values (i.e., curd firmness) were higher for samples with higher protein content. Statistically there was no effect of method of concentration on a40; however subjective analysis of curds during cheese making indicated that CM curds were firmer than UF curds. T0 further evaluate the discrepancy in coagulum characteristics, viscosity during coagulation was monitored. Samples of milk were inoculated with starter culture; each treatment was inoculated with two levels of rennet (132 and 192 μL·kg−1); and changes in viscosity were determined throughout coagulation using Brookfield viscometer. Calculated coagulum strength varied from 2.72 to 9.22 N·m; and increased as protein level increased. Also, CM curd was firmer than its UF counterpart. A higher rate of inoculation of rennet can reduce coagulum strength; however the rate should be optimized to avoid decreasing coagulation time to an unacceptable level.

Investigation of the Colloidal Interactions at Play in Combined Acidification and Rennet of Different Heat-Treated Milks

The properties of gels obtained by combined acidification and rennet were investigated for milks heated at different temperature-time regimes using a high temperature short time (HTST) pilot plant system. Increasing amounts of heat-induced whey protein complexes were found in the soluble phase as a function of heating time/temperature, and only in the most extensively heated milk (i.e., 85 degrees C/300 s), these complexes were in quantities comparable to those reported in previous studies. Two levels of rennet were studied, and at the gelation pH, the amount of CMP released was 11 +/- 1% and 26 +/- 5% in the low and high rennet experiments, respectively. These two levels of rennet caused profound changes in the gelation behavior and in the structure development of the network. When a small amount of rennet was used, different heating temperature-time regimes did not affect the first stage of renneting. Increasing the extent of milk heat treatment and/or the level of rennet increased the pH of gelation and the stiffness of the gels. This work is the first to compare the effect of heating (using a pilot plant setup) and amount of rennet on the destabilization and interaction of casein micelles during aggregation by combined rennet and acidification.

INFLUENCE OF RENNET CONCENTRATION ON RIPENING CHARACTERISTICS OF HALLOUMI CHEESE

ABSTRACT In this study, the influence of rennet concentration on chemical composition, proteolysis and sensory properties of Halloumi cheese was evaluated during ripening. Halloumi cheese was manufactured from raw cow's milk using four levels of rennet (0.2, 0.25, 0.3 or 0.4 g rennet/kg cheese milk) and was ripened for 60 days at 4C. Proteolysis in the cheese was measured by determining soluble nitrogen fractions both in water and in 12% trichloroacetic acid as well as by patterns of urea–polyacrylamide gel electrophoresis. Cheese grading was performed by an expert panel throughout the ripening period. The chemical composition of the cheese was significantly influenced by the level of rennet, which could be related to the differences in moisture contents of the cheese. The levels of water- or 12% trichloroacetic acid-soluble nitrogen fractions and degradations of αs1- or β-caseins were quite low during the cheese maturation. No relation was found between rennet concentrations and casein degradation in the cheese during ripening. Results indicated that the different concentrations of rennet did not significantly influence the proteolytic profiles and sensory scores of Halloumi cheese; that is, an amount of rennet between 0.2 and 0.4 g rennet/kg cheese milk resulted in a similar quality of Halloumi cheese. PRACTICAL APPLICATIONS Halloumi cheese was manufactured from raw cow's milk using different concentrations of rennet and was ripened for 60 days. The chemical composition of the cheese was influenced by different concentrations of rennet; however, ripening indices (proteolysis) and sensory attributes were identical in all samples. It is concluded that different concentrations of rennet (0.2–0.4 g rennet/kg cheese milk) have no significant influence on the ripening characteristics of Halloumi.

Optimizing Sensorial Quality of Iranian White Brine Cheese Using Response Surface Methodology

ABSTRACT: Response surface methodology was used to evaluate the effects of processing variables, such as ripening time (20 to 60 d), ripening temperature (6 to 10°C), level of rennet added (1 to 2 g/100 kg milk), and brine concentration (8% to 14%, w/v), on the sensorial quality of Iranian pickled cheese (feta type). Optimization of sensorial quality was performed by canonical analysis to derive the stationary point. Based on contour plots and canonical analysis, optimum conditions were ripening time 32 d, ripening temperature 8.3°C, level of rennet added 1.6 g/100 kg of milk, and brine concentration 11%. Predicted sensory score was 20.76 from maximum score of 25.

Modeling of proteolysis and lipolysis in Iranian white brine cheese

The simultaneous effects of processing variables such as ripening time (20–60 days), ripening temperature (6–10 °C), level of rennet added (1–2 g/100 kg milk) and brine concentration (8–14%, w/v) on the proteolysis, lipolysis and sensory score of Iranian white brined cheese (Feta type) were explored by the means of response surface methodology. The most important effect in proteolytical terms was produced by ripening temperature and ripening time in linear form, but level of rennet added and brine concentration were also significant at the 5% level. In terms of lipolysis, ripening time was dominant factor in both linear and quadratic forms; quadratic effect of ripening temperature was greater than its linear effect. Based on sensory score, optimum conditions were: ripening temperature = 6.7 °C, ripening time = 49.5 days, level of rennet added = 1.4 g/100 kg of milk and brine concentration = 10.9%, w/v.

Vatless Manufacturing of Low-Moisture Part-Skim Mozzarella Cheese from Highly Concentrated Skim Milk Microfiltration Retentates

Low-moisture, part-skim (LMPS) Mozzarella cheeses were made from concentration factor (CF) 6, 7, 8, and 9, pH 6.0 skim milk microfiltration (MF) retentates using a vatless cheese-making process. The compositional and proteolytic effects of cheese made from 4 CF retentates were evaluated as well as their functional properties (meltability and stretchability). Pasteurized skim milk was microfiltered using a 0.1-μm ceramic membrane at 50°C to a retentate CF of 6, 7, 8, and 9. An appropriate amount of cream was added to achieve a constant casein:fat ratio in the 4 cheesemilks. The ratio of rennet to casein was also kept constant in the 4 cheesemilks. The compositional characteristics of the cheeses made from MF retentates did not vary with retentate CF and were within the legal range for LMPS Mozzarella cheese. The observed reduction in whey drained was greater than 90% in the cheese making from the 4 CF retentates studied. The development of proteolytic and functional characteristics was slower in the MF cheeses than in the commercial samples that were used for comparison due to the absence of starter culture, the lower level of rennet used, and the inhibition of cheese proteolysis due to the inhibitory effect of residual whey proteins retained in the MF retentates, particularly high molecular weight fractions.

Lamb rennet paste in ovine cheese manufacture. Lipolysis and flavour

Abstract In a preliminary study with commercial ewe's milk cheeses, there were statistically significant differences in the sensory evaluation scores and the amounts of short-chain (C4–C10) free fatty acids (FFAs) between cheeses made with lamb rennet paste or bovine rennet. Experimental ewe's milk cheeses were manufactured with 2 levels of artisanally produced lamb rennet paste and 2 levels of bovine rennet in 50 L vats, with a manufacturing replicate done within 1 week. Total coagulating activity was 2500 RU for cheeses manufactured with a high amount of rennet or 1000 RU for cheeses manufactured with a low amount of rennet. The two batches of lamb rennet pastes used had 4.0 (early Spring) and 6.5 U g−1 lipase (late Spring), whereas no lipase activity was detected in bovine rennets. The total concentration of FFAs in cheeses manufactured with lamb rennet paste was significantly higher than in cheeses manufactured with bovine rennet, regardless of ripening time and time of the year. Lipolysis in the former cheeses increased with the total units of lipolytic activity added. The increase in lipolysis in cheeses made with lamb rennet was primarily due to higher amounts of short-chain fatty acids (C4–C10). Butyric acid was the main FFA in cheeses made with lamb rennet paste, representing 34.5 μmol 100 μmol−1 (low level of rennet) and 44.2 μmol 100 μmol−1 (high level of rennet) of the total FFAs, whereas it represented only 17 μmol 100 μmol−1 of the total FFAs in all cheeses made with bovine rennet. The concentration of individual FFAs of chain length

The effect of plasmin activity and cold storage of cheese milk on the composition, ripening and functionality of mozzarella‐type cheese

The effects of casein hydrolysis by plasmin on composition, ripening and functionality in mozzarella‐type cheese were studied. Milk was stored at 4°C for 0, 24 and 48 h, with and without added plasmin, before batch pasteurization and the manufacturing of mozzarella‐type cheese. In parallel experiments, the effects of incubation of milk with added plasmin for 2 h at 37°C prior to cheese manufacture and of an increase in the level of rennet added during cheesemaking were studied. Plasmin addition adversely affected the rennet coagulation properties of the milk and led to increased (two‐ to three‐fold) plasmin activity in cheese and greater plasmin‐associated hydrolysis of β‐casein to γ‐caseins during ripening. Melted cheese flow rate and stretchability increased over ripening and melting time decreased, but functional properties were not affected by either plasmin activity or cold storage. Overall, neither plasmin activity (at the levels studied) nor cold storage greatly affected the composition or functionality of mozzarella‐type cheese.

Proteolysis and its role in relation to texture of Feta cheese made from ultrafiltered milk with different amounts of rennet

The relationship between proteolysis and texture in Feta-type cheese made from ultrafiltered cows' milk was studied using capillary electrophoresis, chemical analysis and uniaxial compression. For this purpose cheeses were made with almost identical gross chemical compositions, but wide variations in texture, obtained by varying the amount of rennet and the coagulation conditions. αs1-Casein (CN) 8P, αs1-CN 9P and αs1-CN 8P-I were degraded during ripening, while β-CN A1, β-CN A2 and para-κ-CN were slightly degraded at the highest rennet additions and longest storage time tested (39 weeks). αs1-CN 8P, αs1-CN 9P and αs1-CN 8P-I were degraded even in cheeses made without rennet, and this was ascribed to cathepsin D activity. αs1-CN 9P disappeared faster than αs1-CN 8P, which suggests that milk acid phosphatase was active during storage. During ripening, stress at fracture (σf), strain at fracture (εf), the deformability modulus (E) and work to fracture (Wf) all decreased. Since the gross chemical composition was essentially constant during storage, these changes could be ascribed purely to proteolysis. Although εf could be predicted fairly well from capillary electrophoresis results (correlation coefficient 0·85), there were no unique relationships between degradation of casein components and σf when both storage time and the amount of rennet used were varied. In the young cheese a high level of proteolysis could coexist with high values of σf. This suggests that high levels of rennet caused σf to increase, via an effect unrelated to general proteolysis, whereas general proteolysis caused the reverse effect.

Physicochemical characteristics and rennet coagulation time of ultrafiltered goat milk

Goat skim milk was concentrated by ultrafiltration (UF) to volume concentration ratios (VCR) of 2, 3, 4 and 5. Gross composition, titratable acidity, pH, nitrogen distribution, percentage retention and recovery of components and rennet coagulation time (RCT) of skim milk during UF processing were studied. During UF of goat skim milk, all fat, CN, WPN, 19% of NPN, 78.1% of TS, 78.6% of ash and 3.5% of lactose were retained in 5-VCR retentate. Recovery of these components were 14.7, 53, 48, 17 for NPN, TS, ash, lactose and 100% for fat, WPN or CN, respectively. For TN, TS, ash, NPN and lactose, retention was increased by increasing the VCR. The titratable acidity was increased from an initial value of 0.14 to 0.38% in 5-VCR retentate, whereas pH decreased from 6.58 to 6.50. The RCT decreased as the protein concentration of the milk increased, but the precise influence of protein concentration decreased at higher levels of rennet.

The influence of phage-assisted lysis of Lactococcus lactis subsp. lactis ML8 on cheddar cheese ripening

Cheddar cheese was made with Lactococcus lactis subsp. lactis strain ML8 as starter and two levels of rennet and three levels of homologous phage. The use of the different phage levels in cheese milk resulted in various degrees of starter lysis early in the ripening process. The levels of activity of two starter cytoplasmic enzymes, lysylaminopeptidase and FBP-aldolase, in the cheese matrix were used as a direct measure of lysis and increased with the level of phage added. Elevated starter lysis was associated with an increased rate of formation of amino acids and ammonia but the removal rate of lactose in the cheese was decreased. The relative levels of hydrophobic and hydrophilic peptides in aqueous cheese extracts were also influenced by the extent of starter lysis. Bitter flavour was prominent in cheese with high rennet concentration, but not when there was also high starter lysis. The results suggest that a balance of lysed and intact cells is important for control of cheese ripening; enzymes released on cell lysis accelerate the rate-limiting peptidolytic steps and removal of some bitter peptides, while intact cells are required for lactose removal. The consequences of the relative levels of intact and lysed cells on substrate-enzyme interactions, enzyme stability and flavour profiles are discussed.

Effects of Reducing Rennet and Adding Calcium Chloride on the Manufacture and Curing of Cheddar Cheese1,2

Summary This study showed the lack of real benefits derived from using low levels of rennet with added calcium chloride in the manufacture of Cheddar cheese. Cheese was made from raw and pasteurized milk during four seasons. Each lot of cheese consisted of three vats to which 90, 45, and 45ml. rennet per 1,000lb. of milk was added, respectively. The third vat of milk was further treated with 0.02% calcium chloride. The cheese was cured at 50° F. for 36 wk. Using subnormal amounts of rennet delayed curd formation in both raw and pasteurized milk. Adding 0.02% calcium chloride with one-half normal amounts of rennet gave normal curd formation and yield, but protein breakdown was slow, and curdiness persisted longer in the finished cheese. The quality of the cured cheese was not influenced by variations in the rennet and calcium chloride used, but persistence of curdiness was undesirable in young cheese made with reduced levels of rennet, especially when supplemented with calcium chloride.